Consolidated bodies of different aluminous metals to provide corrosion protection and method of making



Nov. 26, 1968 T s. DAUGHERTY 3,413,101

CONSOLIDATED BODIES OF DIFFERENT ALUMINOUS METALS TO PROVIDE CORROSION PROTECTION AND METHOD OF MAKING Filed June 10, 1965 INVENTOR T STEVENS DAUGHERTY ATTORNEY United States Patent 3,413,101 CONSOLIDATED BODIES OF DIFFERENT ALUMI- NOUS METALS TO PROVIDE CORROSION PRO- TECTION AND METHOD OF MAKlNG T. Stevens Daugherty, 'Chesterfield County, Va., assignor to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Continuation-in-part of application Ser. No. 375,792, June 17, 1964, which is a continuation-in-part of application Ser. No. 180,401, Mar. 9, 1962, which in turn is a continuation-in-part of application Ser. No. 768,686, Oct. 21, 1958. This application June 10, 1965, Ser. No. 462,996

Claims. (Cl. 29182) ABSTRACT OF THE DISCLOSURE Protecting metals and alloys from corrosion by dispersing an anodic metal therein, including the use of a method which involves compacting and working metal particles.

This application relates to protecting metals and alloys from corrosion, and is a continuation-in-part of U.S. application Ser. No. 375,792 filed June 17, 1964 (now U.S. Patent 3,290,145), which in turn was a continuationin-part of U.S. application Ser. No. 180,401 filed Mar. 9, 1962 now abandoned, which in turn was a continuationin-part of U.S. application Ser. No. 768,686 filed Oct. 21, 1958, and now U.S. Patent No. 3,076,706.

It is known that in order to protect aluminous metals from corrosion, and especially from electrolytic corrosion, such aluminous metals may be coated or clad with a layer of a different aluminous metal which is anodic with respect to the metal to be protected, i.e., which is more electronegative or has a higher electrode potential than said metal to be protected. (Solution potentials of various metal compositions are commonly measured in a one normal sodium chloride solution containing 0.3% hydrogen peroxide, against a one-tenth normal calomel electrode.) In the resulting composite materials, the cladding metal is preferentially attacked and thereby becomes sacrificial to protect the other metal. One or more surfaces of the metal to be protected may be clad, the customary total thickness of the cladding being about 2% to 10% of the thickness of the composite.

Fabrication of such clad or coated metals is more timeconsuming, complicated, and expensive than the fabrication of ordinary metal products, because thick sheets of a the cladding metal must be applied to the base metal to form a sandwich prior to rolling into the finished product. Another disadvantage of such clad products is that the subsequent welding thereof frequently produces de fects, since the cladding metal may melt and flow completely through the weld, thereby providing a path for corrosion which could ultimately completely penetrate the product.

The present invention avoids the need for cladding or coating the base metal by providing a sacrifically protected product having discrete quantities of the anodic metal dispersed within quantities of the metal to be protected, and by further providing a method for conveniently producing such a product.

For a better understanding of the invention, and of its other details, objects, and advantages, reference is now made to the accompanying drawing, which shows, for purposes of illustration only, a present preferred embodiment of the invention. Specifically, the sole figure of drawing is a transverse view of a section of the product showing exposed quantities 10 of the discrete quantities 3,413,101 Patented Nov. 26, 1968 of anodic metal randomly dispersed within the metal 12 to be protected.

Each exposed discrete quantity 10 of the randomly dispersed anodic metal acts as an independent sacrificial anode, thereby distributing the corrosive attack substantially uniformly across all surfaces of the product. Of course, this does not necessarily limit the corrosive attack to the thickness of the cladding material, as does the conventional cladding metal in a conventional clad product. On the other hand, the product according to the present invention is substantially more resistant to excessive pitting and ultimate perforation caused by corrosion than is a homogeneous product made entirely of the metal which otherwise would be protected.

Suitable metals which may be employed in the invention include the conventional aluminum cladding and protected alloy combinations; for example: 6003 alloy dispersed within 2014 alloy; 1230 alloy dispersed within 2024 alloy; 7072 alloy dispersed within any one of 3003, 3004, 5050, 5155, 6061, 7075, or 7178 alloys; or 6253 dispersed within 5056 alloy.

Although the content of the anodic metal in the composite may vary over a relatively wide range, for example, up to 10%, while still affording sacrificial protection, it has been found that lower proportions, for example, 5% and below, are more satisfactory because the statistical probability that quantities of anodic material will be superimposed in contact one upon the other is decreased, thereby tending to limit the penetration of the corrosion to the thick %ess of one such quantity. The actual preferred anodic meta content will of course vary with the difference in the solution potentials of the particular metals used for the composite. In the case of a particular example set forth below, wherein 7072 aluminum alloy is the anodic metal and 5050 aluminum alloy is the metal to to be protected, the preferred anodic material content is about 1% or less.

The article of the present invention may be produced by any convenient mechanical forming process, for example, rolling, extruding forging, and the like. In order to insure its random distribution, the anodic metal is preferably introduced in the form of discrete particles. When the article is desired to be of aluminous metals in the form of a strip or sheet, both the anodic metal and the metal to be protected may be conveniently mixed and rolled continuously into the fully densified product in accordance with the processes described in the aboveidentified patent applications. Since these processes utilize spherical or acicular particles ranging in size from 200 to 10 mesh, the resultant product according to the present invention will contain discrete quantities of anodic metal ranging in volume from 0.05 X 10 cu. in. to 11,000 10* cu. in. As shown in the drawing, these quantities will have a relatively large cross-section in the plane parallel to the strip major surfaces and a relatively small cross-section in planes perpendicular thereto. In the final product, the original particles of both the anodic metal and the metal to be protected will have been thoroughly crushed, compacted, and welded together, with any previous oxide coating therebetween so widely dispersed as to be inconsequential.

The invention is further illustrated in the following examples.

Example 1 A mixture of 95% 6061 aluminum alloy particles and 5% 7072 aluminum alloy particles was compacted into multi-alloy strip in accordance with the processes described in the aforesaid patent applications. A compacted multi-alloy strip of 6061 aluminum alloy and 10% 7072 was similarly produced. Samples taken from these strips, together with control samples of conventional 3003 aluminum alloy, were exposed to city tap water, using intermittent alternate immersion, for 1, 3, and 6 month periods, after which they were removed and the average weight loss and the average maximum pit depth de- Average of two samples having values of 15.0 and 9.0.

Example 2 Four different mixtures of 5050 aluminum alloy particles and 7072 aluminum alloy particles were compacted into multi-alloy strip in accordance with the processes described in the aforesaid patent applications. The 7072 aluminum alloy content was respectively 1%, 3%, 5%, and 7%, with the balance being the 5050 aluminum alloy. Samples taken from these strips, which were all 55 mils thick, together with control samples of conventional 3003 aluminum alloy and 5050 aluminum alloy, in the form of l /z" 8" strips, were degreased in acetone, weighed, and exposed in flush tanks to alternate immersion in city tap water for 3, 6, and 12 month periods, then removed, cleaned in concentrated nitric acid, and the median weight loss and the median maximum pit depth determined. The results are shown in the following table:

93%5050; 7% 7072 (55 mils thickness) 3 182. 7 12. 6 275. 8 13. 12 610. 0 35. 0

3003 (0.15% Cu) (31 mils thickness) 3 90. 2 (1) s 284. e

5050 (65 mils thickness) 3 46.9 30. 0 6 170. 7 46. 0 12 489. 6 52. 0

5050 (60 mils thickness) 3 47. 6 22. 0 6 124. 7 37. 0 12 368. 4 44. 0

5050 (51 mils thickness) 3 63. 5 31. 0 6 316.0 48. 0 12 466. 5

1 Perforated.

While present preferred embodiments of the invention have been illustrated and described, it will be understood that the invention may be otherwise variously embodied and practiced within the scope of the following claims.

What is claimed is:

1. A metal article of improved resistance to corrosion, comprising a consolidated particulate mass having particles of a first aluminous metal and particles of a second aluminous metal which are anodic with respect to said first metal particles, wherein said particles of the second metal are dispersed among the first metal particles in a proportion no greater than 10%, thereby providing sacrificial protection for said first metal.

2. The article according to claim 1 wherein said first metal is an aluminum alloy.

3. The article according to claim 1 wherein particles of said second metal are randomly dispersed within said first metal.

4. The article according to claim 1 wherein particles of said second metal and particles of said first metal are thoroughly welded together.

5. The article according to claim 1 wherein substantially all of said particles of said second metal have volumes in the range of from 0.05 10* cu. in. to 1l,000 10 cu. in.

6. The article according to claim 1 wherein substantially all of said metal particles range in size from 200 to 10 mesh.

7. The article according to claim 1 wherein said second metal is an aluminum alloy.

8. The article according to claim 1 wherein said second metal is an aluminous cladding alloy and said first metal is an aluminous alloy sacrificially protected by said second alloy.

9. The method of producing a metal article having improved resistance to corrosion, comprising the step of: compacting and working a particulate mixture comprising particles of a first aluminous metal, and particles of a second aluminous metal which is anodic with respect to said first metal, thereby producing a consolidated particulate mass containing discrete quantities of said second metal dispersed within and thoroughly welded to said first metal.

10. A metal article of improved resistance to corrosion, comprising a consolidated particulate mass consisting essentially of particles of a first aluminous metal and particles of a second aluminous metal which are anodic with respect to said first metal particles, wherein said particles of the second metal are dispersed among the first metal particles in a proportion no greater than 10%, thereby providing sacrificial protection for said first metal.

References Cited UNITED STATES PATENTS 2,287,251 6/1942 Jones -200 3,043,754 7/ 1962 Hollingsworth et a1. 3,076,706 2/1963 Daugherty 75-211 3,113,002 12/ 1963 Hollingsworth et a1.

3,184,840 5/1965 Byrne et al 75200 X 3,290,145 12/1966 Daugherty 75-200 X FOREIGN PATENTS 626,764 7/ 1949 Great Britain.

BENJAMIN R; PADGE'IT, Primary Examiner.

R. L. GRUDZIECKI, Assistant Examiner. 

